Apologies if this is a repeat of previous threads, I did search and can't see an answer to my question. I'm a fitness trainer and a subject that comes up with clients from time to time is the physics of the stairmaster. Confusion reigns as some influential commentators have said that it has no exercise value "as the step is falling away". I'm satisfied that they just betray a very incomplete understanding of the physics, as the fact is that so long as the relative positions of the mass and point of application of the force are either forced apart (as in a squat), maintain their distance (as in any isometric exercise or the paused phase at the top and bottom of a squat just before lowering or return) or only allowed to come together at a controlled rate (as in the eccentric phase of a movement or the deliberate slowing of a movement like the squat mid-exercise, or where there is force being applied which is less than the mass, so that the force is overcome and the mass moves anyway) by virtue of the application of muscular force, then work is being done and exercise value is achieved. The fact that most of the mass of the body maintains its position is irrelevant. Besides my understanding of the physics, the fact that anyone using a stairmaster sweats, pants and gets tired is evidence that work is being done. So; Am I broadly correct in my understanding of the physics? If not, what am I missing? Is there any easier way to explain this to clients or a resource I could post them to? TIA for any help, it'll all be appreciated.